Fort St. John, B.C. – The Site C Dam project in B.C. achieved a breakthrough this month. Officials announced that the first of two diversion tunnels broke through on June 22.
Both tunnels will be used to temporarily reroute a brief section of the Peace River to allow for construction of the dam across the main channel of the river. River diversion is scheduled for this September.
The first tunnel is approximately 700 metres long and 12 metres in diameter. Work on the tunnel began last July.
The tunnel was dug using roadheaders to grind away rock and load it on to conveyors. The rock is then hauled away by truck and stored on site.
Crews are now working to line the tunnel using a custom-built slip form where concrete is pumped through small openings located around the slip form. This enables it to cure in a perfect circle outside the form.
Each pour takes two to three days to cure, and the liner thickness can range between 40 centimetres and 200 centimetres. In total, about 41,000 cubic metres of concrete will reinforce the walls of both tunnels.
This work is the last step in the construction of the diversion tunnels prior to river diversion in fall 2020.
BC Hydro anticipates it will break through on the second tunnel next month.
Once operational, the capacity of the two tunnels will be 3,000 cubic metres of water per second. On average, the diversion tunnels will typically pass river flows between 500 and 1,800 cubic metres per second.